Twin-hull sail boats are a form of catamaran that has gained great popularity. Typical components are two hulls, or pontoons, spaced apart by a forward cross-strut and an aft cross-strut, with a deck supported between the hulls. In light-weight models that are commercially available, the deck is sometimes made of fabric stretched between the forward and aft cross-struts, and between frames running parallel to the struts; such a deck is sometimes called a trampoline. A mast, sails and guy lines provide the propulsion system, and two rudder pivoted one at the aft end of each hull provide the steering system. Typically, rudder arms extend forward one from each rudder, and the forward ends of these arms are joined by a tiller cross-link through which the rudders are steered in unison. Boats of this general description are commercially available under such trademarks or names as "Hobe Cat", "Prindle", "Toronado" and "Sole Cat", for example.
Typically, such twin-hull boats respond quickly, and accelerate rapidly in response to the slightest wind but, being light in weight, have little stored momentum and so they just as quickly lose forward motion when the wind dies. In regions where the wind is not constant, or where the wind velocity varies down to nothing from one place to another, they are frequently and easily be-calmed. Yet owing to their light weight and meagre mechanical structures, they afford little or no place to carry a motor for only occasional use, with the result that sailing sometimes gives way to paddling.